Anabolic-androgenic steroids (AAS) are synthetic derivatives of testosterone originally designed for therapeutic uses. Although AAS continue to be used clinically today, the medical benefits of low therapeutic doses of AAS stand in sharp contrast to the potential health risks associated with the excessive doses self-administered by a growing number of recreational users. While the stereotypical AAS user is an adult male, recent studies indicate that the most rapid increases in AAS abuse are in females. In spite of this fact, few studies have assessed AAS effects on behavior in females, and no studies have been performed to test if AAS act through the same signaling mechanisms in the male and female brain. Heightened aggression is the most commonly described psychological effect of AAS use. Signaling mediated by androgen and estrogen receptors (AR and ER) is essential for the expression of innate aggression in both sexes: however the roles of AR and ER in mediating AAS-induced aggression are not known. The first goal of this proposal is to determine the dose-response characteristics of the aggression-promoting effects of a cocktail of commonly abused AAS, how AAS may alter cues important in eliciting aggressive behavior, and the importance of AR and ER signaling in mediating AAS-evoked aggression by experiments using pharmacological inhibitors of AR and ER and using mutant mice that lack functional AR or ER (specifically ERalpha). Importantly, this study will be the first to compare and contrast these effects in male and female mice. Neural transmission mediated by forebrain gamma-aminobutyric acid type A (GABAA) receptors is required for the expression of innate aggression. We have shown that AAS treatment alters forebrain GABAA receptor expression and function, but does so differently in male and female mice. The second goal of this proposal is to determine the dose-response characteristics for AAS-dependent changes in GABAA receptors in forebrain regions critical for the expression of aggression, the importance of AR and ER signaling in mediating those changes, and to further establish how the effects of AAS on forebrain GABAA receptors differ between male and female mice. To date over 60 AAS have been synthesized that vary in their estrogenic and androgenic properties. Data from these experiments will have important implications for understanding the effects each of these abused AAS may have on untoward aggression and if they will act differently in men and women. These data will also provide important new information on the mechanisms by which AAS elicit changes in synaptic transmission that may contribute to AAS-induced aggression in both the male and female brain. Such data may be relevant towards understanding not only the effects of AAS, but of other abused drugs that act via GABAergic pathways.